1. Field of the Invention
The present invention relates to an antenna element for use in reception or transmission of radio waves, and more particularly, to an antenna element which has conductors formed on its outer surfaces of a device substrate.
2. Description of the Related Art
At present, radio communication apparatuses called a mobile telephone and the like are pervasive in general users, and a reduction in size and weight is required for the radio communication apparatuses. The radio communication apparatus receives and transmits radio waves through an antenna element, where the total length of a conductive path is closely related to the wavelength of a radio wave transmitted or received thereby.
For this reason, since a simple reduction in the length of the conductive path causes a rise in the resonant frequency, difficulties are encountered in efficiently radio communicating a radio wave at a predetermined frequency. To address this problem, a variety of techniques have been devised for reducing the shape of an overall antenna element while maintaining a required resonant frequency.
For example, an antenna element called a helical antenna has a conductive path formed in a spiral shape, while an antenna element called a meander antenna has a conductive path in a meandering shape. While these antennas do not achieve a reduction in the total length of the conductive path, the overall shape can be substantially reduced.
There is also an antenna element called a dielectric antenna which has a conductive path formed on the surface of a dielectric material to reduce the length of the conductive path. Since the wavelength of a radio wave is reduced within a member having a high dielectric constant or permeability, the formation of the conductive path on or within a dielectric material or a magnetic material results in a reduction in the total length thereof.
Moreover, there is an antenna element called a loaded antenna which adds a reactance element, an inductance element or a capacitance element to a conductive path to reduce the length of the conductive path. It should be understood that a variety of foregoing techniques may be combined, for example, to create an antenna element which has a conductive path formed in a helical shape or in a meander shape on the surface of a dielectric material.
An antenna element can be made compact by a variety of techniques as described above. However, in the helical antenna and meander antenna, a long conductive path is bent to reduce the area occupied thereby, so that adjacent portions of the conductive path are electromagnetically coupled to cause an increase in surface current and high frequency loss.
To solve the problem as mentioned, the present inventor invented an antenna element which has a conductive path formed in a shape different from the helical shape or meander shape on the surface of a dielectric material, and filed the invention as Japanese Patent Application No. 2001-026002. This application discloses an antenna element which has a first conductor and a second conductor, parallel to each other, connected by a short-circuit conductor to form a loaded inductance.
Referring now to FIG. 1, the antenna element disclosed in the application will be described below in brief, as a related art which precedes the present invention and is not known. The antenna element described below was filed in Japan on Feb. 1, 2001 as Japanese Patent Application No. 2001-026002, and filed in the United States of America on Jan. 31, 2002 as U.S. Ser. No. 10/059423 by the present inventor. However, this application has not been opened in any country, so that this is not a prior art but merely a related art of the present invention.
Antenna element 100 in the aforementioned application has device substrate 101 made of a dielectric material in rectangular solid, and conductive path 102 formed of a printed wire on the front surface of device substrate 101 to implement a dielectric antenna as described above. Conductive path 102 is comprised of power supply conductor 103, first conductor 104, short-circuit conductor 105, and second conductor 106.
More specifically, power supply conductor 103 of conductive path 102 comprises a linear portion formed from the bottom surface to front surface of device substrate 101, while first conductor 104 comprises a linear portion formed from an upper end or terminate end of power supply conductor 103 and bent at a right angle to the right in the figure.
Short-circuit conductor 105 comprises a linear portion formed from a right end or terminate end of first conductor 104 and bent upward at a right angle in the figure, i.e., in the opposite direction to power supply conductor 103, while second conductor 106 comprises a linear portion formed from an upper end or terminate end of short-circuit conductor 105 and bent at a right angle to the left in the figure, and positioned in parallel with first conductor 104.
In antenna element 100 of the structure as described, conductive path 102 can be reduced in length since first conductor 104 and second conductor 106, positioned in parallel with each other, act as a loaded inductance. In addition, since conductive path 102 is generally bent in a U-shape (which has three straight lines forming two right angles), the overall shape can be made compact.
Unlike the meander antenna, helical antenna and the like, in spite of the reduction in size, first conductor 104 and second conductor 106, positioned in parallel with each other, are sufficiently spaced away from each other, so that their electromagnetic coupling is reduced, thereby making it possible to realize radio communications with high gain, high efficiency and wide band.
Antenna element 100 of the structure described above presents a rise in the resonant frequency as the overall shape is simply reduced in shape, whereas the resonant frequency is reduced as the loaded inductance is increased. In other words, when the resonant frequency is maintained constant, an increase in the loaded inductance can result in a relative reduction in the size of the overall shape.
The loaded inductance of conductive path 102 in the aforementioned antenna element 100 may be increased by spacing first conductor 104 and second conductor 106 away from each other, reducing the width of conductive path 102, extending the length of conductive path 102 such as first/second conductors 104, 106, and the like.
However, for spacing first conductor 104 and second conductor 106 away from each other, device substrate 101 must be extended, resulting in an increased size of the overall shape. The width of conductive path 102 has a lower limit determined by a thermal condition, and a reduction in the width of the conductive path 102 will cause a reduced bandwidth and an increased high frequency loss, so that the width of conductive path 102 cannot be reduced without prudence.
It is an object of the present invention to provide a antenna element which is made compact, and has a first conductor and a second conductor positioned in parallel with each other and connected through a short-circuit conductor.
The antenna element according to the present invention has a first conductor, a short-circuit conductor, a second conductor, and a device substrate. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the first conductor, short-circuit conductor and second conductor on its outer surface. The first conductor is made of a linear conductor supplied with electric power at a leading end thereof, while the short-circuit conductor is connected perpendicularly to a terminate end of the first conductor. The second conductor is connected at a right angle to a terminate end of the short-circuit conductor and positioned in parallel with the first conductor.
In a first aspect of the antenna element described above, an extended portion bent in a U-shape is formed in at least one of the first conductor and the second conductor. In a second aspect, the first conductor and second conductor are formed continuously on a plurality of outer surfaces of the device substrate. In a third aspect, the first conductor and second conductor are formed continuously on a plurality of outer surfaces of the device substrate, and an extended portion bent in a U-shape is formed in at least one of the first conductor and second conductor.
Thus, the antenna element of the present invention can extend the conductive path without increasing the size of the device substrate even though the parallel first conductor and second conductor are connected through the short-circuit conductor on the outer surface of the device substrate. It is therefore possible to reduce the size of the device substrate without relatively extending the conductive path, and reduce the size of the overall shape while ensuring a desired resonant frequency.
In another implementation of the antenna element as described above, a power supply conductor is also formed as part of the conductive path. The power supply conductor has a terminate end connected at a right angle to the leading end of the first conductor, and positioned on the opposite side to the short-circuit conductor. By supplying electric power to a leading end of the power supply conductor, the electric power can be supplied to the first conductor from the power supply conductor.
Since the first conductor and second conductor are formed from the front surface to the back surface across one side surface of the device substrate formed in rectangular solid, the conductive path can be extended, effectively making use of a plurality of outer surfaces of the solid device substrate.
Since the first conductor is formed at different positions on the front surface and rear surface of the device substrate, a portion of the first conductor positioned on the front surface of the device substrate can be spaced apart from a portion of the first conductor positioned on the back surface to reduce a distributed capacitance, thereby making it possible to prevent a reduction in the bandwidth of communication frequencies due to accumulation of unwanted electromagnetic energy.
Since the second conductor is formed at different positions on the front surface and rear surface of the device substrate, a portion of the second conductor positioned on the front surface of the device substrate can be spaced apart from a portion of the second conductor positioned on the back surface to reduce a distributed capacitance, thereby making it possible to prevent a reduction in the bandwidth of communication frequencies due to accumulation of unwanted electromagnetic energy.
Also, by virtue of:
a conductive pathar connection of a leading end of the extended portion formed and connected to the leading end of the first conductor to a terminate end of the power supply conductor;
a linear connection of a terminate end of the extended portion formed and connected to the terminate end of the first conductor to a leading end of the short-circuit conductor;
a linear connection of the leading end of the extended portion formed and connected to the leading end of the second conductor to a terminate end of the short-circuit conductor; and
a linear connection of the terminate end of the extended portion formed and connected to the terminate end of the second conductor to a leading end of a connection conductor,
the shape can be simplified, even though the conductive path is extended, thus making it possible to improve the productivity of the antenna element.
Since a capacitive conductor having a given capacitance is connected to the terminate end of the second conductor, the conductive path can be reduced in length due to a capacitance load of the capacitive conductor.
Since the second conductor is formed integrally with a capacitive conductor of a given capacitance, the conductive path is reduced in length due to a capacitance load of the capacitive conductor. Since the capacitive conductor and second conductor need not be separately formed and connected to each other through a connection conductor, it is possible to simplify the structure to improve the productivity, and reduce the size of the overall shape.
Since a resonant circuit is formed of a resonant conductor formed at a predetermined position of at least one of the first conductor and second conductor to the vicinity of the other one, the resonant circuit permits the antenna element to support radio communications at a plurality of frequencies, making it possible to improve the performance of the antenna element.
Since a plurality of resonant conductors are connected respectively to at least one of the first conductor and second conductor, a plurality of resonant circuits resonate at different frequencies from one another, permitting the antenna element to support radio communications at a plurality of frequencies and at frequencies in a wide band.
A radio communication apparatus according to the present invention, with the provision of the antenna element of the present invention, can radio communicate a radio wave at a desired frequency through the small antenna element.
The above and other objects, features and advantages of the present invention will become apparent from-the following description with reference to the accompanying drawings which illustrate examples of the present invention.